Recently, there has been growing interest in energy storage technologies. As energy storage technologies are extended to devices such as cellular phones, camcorders and notebook PC, and further to electric vehicles, demand for high energy density of batteries used as a source of power supply of such devices is increasing. Therefore, research and development of lithium secondary batteries, which most meet the demand, are actively being conducted.
As well known in the art, conventional lithium secondary batteries have a cathode made of lithium-containing oxide and an anode made of carbon-based materials, which can intercalate or disintercalate lithium ions, a separator for acting as a bridge between the anode and the cathode to prevent an electrical contact therebetween, and a non-aqueous electrolyte.
Also, in the case that such a battery is manufactured in a prismatic form, it further has a safety vent which exhausts a great deal of gas generated from the decomposition of the non-aqueous electrolyte during the abnormal operation of the battery, e.g., overcharging, thereby preventing an additional explosion and/or ignition.
FIGS. 1 to 3 show a safety vent which is formed at a side of the case of prismatic batteries and has a closed or partially opened groove.
In FIG. 1, a safety vent 10 is formed on an outer surface of a prismatic secondary battery case 20 in a large contour corresponding to the rectangular side shape of the case, and has a groove 30 formed along such a contour, i.e., a closed groove. In contrast, safety vents 12 and 14, as shown in FIGS. 2 and 3, respectively, are formed in the corner on a side of a battery case in a small contour, and each of them have a partially opened groove 30.
If an excessive amount of gas is generated inside of the battery due to overcharging, the groove 30 is cut by the internal pressure of the battery to form a vent hole (the opening of the vent hole), from which internal gas is exhausted outward to prevent the explosion or ignition of the battery.
However, the safety vent should not open due to its excessive sensitiveness even when there is no danger of explosion and/or ignition since the gas generated in the battery is combustible and harmful, and thus may induce environmental problems.
Accordingly, there is a need to develop a lithium secondary battery having a non-aqueous solution capable of reducing gas generation and a safety vent capable of properly operating when the battery operates abnormally due to overcharging.